Tungsten metal and process for making the same



Patented Apr. 20, 1937 PATENT OFFICE TUNGSTEN METAL AND PROCESS FORMAKING THE SAME- Chester 11. Braselton, New York, N. Y., assignor toSirian Wire and Contact Company, Newark, N. J., a corporation ofDelaware No Drawing.

32 Claims.

This invention relates to a process of metal -manufacture and productsresulting therefrom. More particularly, the invention pertains totreatment of tungsten and allied refractory metals so as to make themmore suitable for use as filaments in lamps or other radiating devices.

Refractory metals such as tungsten when employed as filaments forelectric lamps are subject to an internal alteration which brings abouta deformation called sagging and which is detrimental to lampefliciency. It has been proposed to remedy this defect by introductionof foreign substances which modify or control the crystal growth of thefilament metal. Certain disadvantages result from this treatment, suchas deposition of the foreign substance on the inner surface of theenvelope.

I have discovered that resistance to internal alteration of the metalmay be developed by introducing into the metal, particles of the samemetal but derived from different sources so that in the completedmetalthere is a structure composed or large and small particles of the samemetal, all of the particles being intimately bound together. In additionI have found that if in the process of forming the final metal theparticles are amalgamated by a chemically deposited bond of the samemetal a marked improvement in resistance to deformation of the finalstructure results.

It is an object, therefore, of my inventionto provide a process formaking metal for filaments and other uses which will not requireintroduction of foreign particles as permanent constituents of themetal; which introduces new methods of developing resistance againstchange of shape and structure of the metal when heated; which permitsformation of particles of different size of the some metal withoutsubjecting the particles 40 of the metal to diiferent heat treatment andwhich establishes an effective bond between the various particles of themetal.

Further objects of the invention are to provide 7 a refractory lampfilament, the desirable properties of which are not impaired by themanufacturing operation or by subsequent use, and to improve in generalthe efliciency and life 0 tungsten lamp filaments.

Still other objects are to provide a form of metal which issubstantially independent of the crystalline structure for its physicalpermanency of shape; to provide a refractory filamentary metal whichwhile homogeneous; isformed of particles of different size; and toprovide a filament of tungsten, molybdenum or other refrac- ApplicationDecember 29, 1934, Serial N0. 759,693

tory metal which is not subject to substantial impairment in physical orelectrical properties when operated at-high temperature.

Further objects will be apparent on consideration of the followingdescription of the process and of the product produced thereby.

In practicing my invention, which I will describe with reference to themetal tungsten, I employ as a primary source of this metal, tungstentrioxide (W03),- which in turn may be derived 10 from the hydratedtungstic oxide having a formula approximately H2WO4. As a secondarysource of tungsten I may utilize any of the well known alkalinetungstates, such as the tungstates of potassium, lithium, sodium,rubidium and caesium. These tungstates may be in any of the variousforms in which they occur, such as the normal or.ortho-tungstates havingthe formula generally accepted as M2WO4, the meta-tungstates having theformula M2W4Ol3'alld the para- 20 tungstates having the formula eitherM1oW12O41 or M6W7O24 where M stands for any alkaline metal.

For the purpose of illustrating the various steps of the processtungstic acid and potassium tungstate will be utilized in thedescription. These 25 compounds in chemically pure state are mixedtogether, the tungstic acid being added to a solution of the tungstatein distilled water and the mixture then heated to drive off the excessof water. As an example, I may use one kilogram 30 of tungstic acid andsixty-one and one-half grams of pure potassium tungstate orapproximately six percent of the tungstate by'weight of the mix- 'ture.

This mixture of the tungstic acid and potassium 5 tungstate is thenplaced in a crucible and heated to a state of complete dehydration, theresulting product consisting of tungsten trioxide (W03) and postassiumtungstate being ground and bolted through a 200 mesh per inch screen 40I forming tungsten and water and the tungstate forming tungsten, water,and potassium hydrox- 50 ide (KOH).

The reduced product, which is in powdery form, is now mixed with othersimilarly made lots having somewhat difierent densities to obtain'a Hmixture of desired density and then pressed hy- 5 draulically to form aningot having a size approximately x x 16". The ingot is first baked inhydrogen at about 800 C. to permit handling and then suspended in aconduction 5 type electric furnace where current is passed through theingot for a period of about twentynine minutes in hydrogen flowingtwenty cubic feet per hour. By this means the temperature is raisedtoabout 90% of the fusion temperature fortungsten, at which point thetemperature is held about ten minutes. and then permitted to a I drop toroom temperature. In this operation the potassium hydrornde is meltedand volatilized. The molten hydroxide being a ready solvent for tungstenand tungsten oxide carries tungsten in solution. This tungsten isderived from the tungsten oxide carriedv over from the initial lot orformed by oxidation of the pure tungsten between the heating steps. Itis also derived from direct action on the tungsten particles.Accordingly when volatilization occurs the tungsten is deposited on theclean surface of the tungsten particles thus permitting a close bond orweld between the particles and a more solid mass. The 5 metal is nowready for mechanical treatment, and where filamentary wire is desiredthe ingot is swaged and drawn-to the desired diameter.

The reduction heat in which metallic tungsten is produced involves twotungsten compounds but these compounds do not reduce at the sametemperatures, the oxide reducing before the tungstate. Hence. it isapparent that the microscopic structure of the tungsten particlesobtained from the tungsten. trioxide will differ from that of thetungsten particles derived from the tungstate. This difference isevidenced in difierent crystal size, the smaller crystals apparentlyfilling the interstices between the larger crystals so that there isbuilt up a solid and 40 homogeneousmetal mass of approximately uniformdensity. I V The second or volatilization heat in the conduction furnacebegins with all of the tungsten particles encased or surrounded bymasses of potassium hydroxide. The action of the hydroxide apparently isvery similar to a flux or cleaning agent on the one hand, and of asolvent on the other hand. In the fusedform the hydroxide dissolves theoxide and the tungsten itself on the surface ofthe particles etchingand.

roughening the surface. Subsequently the tungsten is deposited from thevolatilizing hydroxide and is fused into and between the roughenedsurfaces thus forming a more rigid mass than would otherwise be possibleand definitely reducing deformation at high temperatures.

a duce ametal structure which at high temperatures deformation and hencemaintains its original and normal physical and electrical properties. Inthis way the electrical efliciency of such a metalfor lamp filaments isimproved and longer life is secured.

The cleansing power of the alkaline hydroxide on the particles of metalmaybe utilized in a modified process which will now be described.

Instead of employing tungstic acid as the oxide constituent, tungstenmetal may be used in par- 0 ticle form in conjunction with the alkalinetung state. In this modified process the tungstate such as potassiumtungstate is dissolved in warm water and to this solution finely dividedmetallic tungsten or other refractory metal is added. The mixture isthen stirred while the temperature is in filamentary form stronglyresists- .2,o77,e7s

slowly raised bringing about evaporation of the water. This material isthen placed in a tube furnace in a flow of hydrogen gas and heated forthree or four hours until the tungstate breaks down to free tungsten andpotassium hydroxide.

' This intermediate product is then removed,

pressed into an ingot, baked at a temperature in excess of 800 C. togive the material rigidity for handling, and then heated as describedin' the preferred process to approximately of the fusion point oftungsten, thus volatiliz'ing the hydroxide and sintering andamalgamating the crystals of metal. A typical batch might includematerials in the relation of 61 grams of .potassium para-tungstate to793 grams'of tungsten.

A modification of the process just mentioned would be to use only thetungstate or an alkaline compound of another refractory metal and reducethe same in a hydrogen flow, continuing the heating process until thehydroxide component is removed leaving pure tungsten.

The same procedure may be utilized with a ,mixture of a. solution'of ahydroxide such as potassium hydroxide and finely divided tungsten orother refractory metal, the water of the solution being evaporated andthe material formed into an ingot which is treated as previouslydescribed by first heating to a temperature in excess of 800 C; toobtain the ingot, and then placing the ingot in an electric conductionfurnace wherein the ingot is raised to a temperature in excess.

of 2000 C. approaching 90% of the fusion point of tungsten. This finalheat treatment volatilizes the hydroxide and sinters the tungstenparticles to form a highly coherent body. These materials may becombined directly by a mechanical tumbling mill operation but theparticles of metal are not as thoroughly coated by the hydroxide aswhere a solution is employed.

In either of the suggested modifications of the process above describedinstead of tungsten metal as one of the component elements otherrefractory metals such as molybdenum. titanium,

tantalum, zirconium or chromium may be used with the tungstate orhydroxide. In the case of the tungstate and a metal other than tungstenthe result will be an alloy of the tungsten.

It'is emphasized that the strength and utility of filaments madeaccording to any of the above processes arises from the apparentcleansing and solvent action of the hydroxide not only on for,- eignparticles such as unreduced particles tungsten trioxide but also onminute particles of tungsten, thereby assuring a clean contact andintimate welding between particles. Further,

theuse only of compounds which by heat treat- The result of this processtherefore is to proment ar either voiatilzed or reduced to metallictungsten eliminates the difficulties arising from the presence oi.foreign matter'such as the silicates.

from 12 to 4'1, and indicating apparently that the absolute size is notthe only determining factor in producing stability.

It is noteworthy also that the completed product consists entirely oftungsten. There are no' other foreign substances present which maygradually modify the metal characteristics during use. The alkalinehydroxide is volatilized at temperatures relatively low with referenceto the Moreover, the intergranular crystal-- 1 line structure arisingfrom tungsten crystals of group such as molybdenum may be used. Also,

not only may any of the various alkaline metal tungstates mentioned beused but also mixtures of these tungstates with each other. Further,other refractory metals such as, molybdenum, chromium, titanium,zirconium or tantalum may be produced from a mixture of the metaloroxide of the metal with a corresponding alkaline metal compound, forexample, molybdenum or molybdenum oxide with an alkaline molybdate. Inaddition, while the specific values givenv are preferred, variations maybe used. For example, the temperature of heat applied tothe metal in thefinal treatment is given as about 90% of the fusion point-of tungsten,but the range may vary according to the determination used. It may bepreferable, therefore, to define this temperature as a temperature-inexcess of 2000" C.

The alkaline metal compound left after the reduction in hydrogen of thetungstic oxide compound and the tungstate is probably either the oxideor the hydroxide which then subsequently is volatilized at a temperatureup to above'2000 C., a portion of the alkali metal or hydroxide possiblybeing removed at temperatures below 2000" C. at least in part.

While I have described what now appears to be a preferred method ofpracticing my invention, setting down specified limits and values, it

should be understood however that these limits and values are merelyillustrative as variations will occur dependent upon the purity of thematerial, time allowed for process, rate of flow or movement and othervariables. I do not wish my invention therefore to be restricted only asrequired by the scope of the claims hereto appended.

What I claim is:

1. The process of obtaining tungsten metal which comprises reducing inhydrogen a mixture of dehydrated tungstic acid and alkali metaltungstate to tungsten and another alkaline compound, forming theresultant product into an ingot, substantially completely volatilizingin hydrogen the alkaline compound of theingot, and mechanically workingthe ingot to size.

2. The process of obtaining tungsten metal which comprises reducing inhydrogen by two successive heating steps a mixture of dehydratedtungstic acid and an alkali metal tungstate to homogeneous metallictungsten, the tungstate being reduced to'a metal and an alkali metaloxide compound in the first heating step and then substantiallycompletely volatilizing the alkali metal oxide compound.

3. The process of obtaining ductile tungsten metal in the form ofaningot capable of producing a drawn tungsten filament withnon-offsetting and non-sagging properties, said ingot consisting oflarge and small particles of the metal cemented together by thin layersof a chemical deposit of the metal which comprises reducing in hydrogena dehydrated powdered mixtureof tungsten trioxide and an alkali metaltungstate, compacting the reduced powder to form an ingot, baking theingot in hydrogen and substantially completely volatilizing theresultant alkaline compound.

4. The process of obtaining ductile tungsten metal in the form of aningot capable of pro-.-

. ducing a drawn tungsten filament with non-oftsetting and non-saggingproperties, said ingot consisting of large and small particles of themetal cemented together by thin layers of a chemical deposit of themetal which comprises reducing in hydrogen dehydrated powdered tungstentrioxide and potassium tungstate, compactmetal in the form of an ingotcapable of producing a drawn tungsten filament-with non-oifsetting andnon-sagging properties, said ingot consisting of large and smallparticles'of the metal cemented together by thin layers of a chemicaldeposit of the metal which comprises reducing in hydrogen dehydratedpowdered tungsten trioxide and sodium tungstate, compacting the reducedpowder to form an ingot, baking the ingot in hydrogen and subsequentlysubstantially completely volatilizing in hydrogen the sodium compoundformed from the reduction step.

6. The process of preparing ductile tungsten metal in the form of aningot capable of producing a drawn tungsten filament with non-offsettingand non-sagging properties, said ingot consisting of 'large and smallparticles of the metal cemented together "by. thin layers of a chemicaldeposit of the metal which comprises reducing in hydrogen dehydratedpowdered tungsten trioxide and caesium tungstate, compacting the reducedpowder to form an ingot, baking the ingot in hydrogen and subsequentlysubstantially completely volatilizing in hydrogen the caesium compoundformed from the reduction step.

7. The process of preparing ductile tungsten metal in the form of aningot capable of producing a drawn tungsten filament with non-offsettingand non-sagging properties, said ingot consisting of large and smallparticles of the metal cemented together by thin layers of a chemicaldeposit of the metal which comprises reducing in hydrogen a dehydratedpowdered mixture of purified tungsten oxide and an alkali metaltungstate in predetermined quantities compacting the reduced powder toform an ingot, baking the ingot in hydrogen and finally elevating thetemperature'after said reduction to a degree where the alkali. metaloxide will substantially completely vaporize, but below the fusion pointof tungsten.

8. The process of preparing ductile tungsten metal in the form of aningot capable of producing a. drawn tungsten filament withnon-oifsetting and non-sagging properties, said ingot consisting oflarge and small particles of the 'metal cemented together by thin layersof a which comprises mixing with tungstic oxide, tungstates of one ormore alkaline metals, reducing the oxide and tungstates, forming thereduced substances in compact form, and subsequently heating thecompacted product to temper-atures below the melting point of tungstenand above 2000 C.

10. The process of producing tungsten metal which comprises mixingtungstic oxide and an alkali metal tungstate, reducing the oxide andtungstate, heating the reduced product in successive stages to atemperature in the neighborhood of 90% of the fusion temperature oftungsten, maintaining said temperature for a period of approximately tenminutes, and subsequently working the metal to form.

11. The process of producing tungsten metal which comprises mixingtungstic oxide with an alkali tungstate, reducing the mixture byapplying heat in fixed increments over a period of approximately twelvehours in a flow of hydrogen gas, subsequently pressing the reducedproduct to ingot form, substantially completely volatilizing substancesforeign to the tungsten in a hydrogen atmosphere, and finally workingthe metal to the form desired.

12. A pure tungsten metal consisting of tungsten particles ofconsiderably difierent sizes, and the particles of said tungsten beingscoured by complete vaporization of alkali metal oxides in combinationtherewith up to an elevated temperature above 2000 C. and below thefusion point of tungsten, said tungsten in filamentary form havingnon-offsetting and non-sagging characteristics, said tungsten consistingof the hydrogen-reduction products of tungsten oxide and an alkali metaltungstate.

13. Pure tungsten metal, the particles of which are of considerablydifferent sizes and intermixed to obtain a uniform metal density, andthe particles of said tungsten being scoured by complete vaporization ofalkali metal oxides in combination therewith up to an elevatedtemperature above 2000 C. and below the fusion point of tungsten,

said tungsten in filamentary form having nonoifsetting and non-saggingcharacteristics, said tungsten consisting of the hydrogen-reductionproducts of tungsten oxide and an alkali metal tungstate.

14. Pure metallic tungsten, the particles of which are of considerablydifferent sizes and de-- rived from plural sources having a greaterstability with greater density when in filamentary.

form than tungsten derived from a -singlesource,

and the particles of said tungsten being scoured by completevaporization of alkali metal oxides in combination therewith up to anelevated temperature above 2000 C. and below the fusion point oftungsten, said tungsten in filamentary 80 form having non-ofisetting andnon-sagging characteristics, said tungsten consisting of thehydrogen-reduction products of tungsten oxide and an alkali metaltungstate.

15. A pure non-sagging, non-offsetting tung- 5 sten filament havingparticles of considerably different sizes, said formations having beenproduced by the reduction of a mixture of tungsten oxide and an alkalimetal tungstate in hydrogen with subsequent complete vaporization of theal- 70 kali metal oxide up to a temperature above 16. The process ofproducing tungsten metal which comprises mixing tungstic acid with lessthan ten percent by weight of normal potassium u tungstate, dehydratingthe mixture, subsequently reducing the mixture in an atmosphere ofhydrogen, substantially completely volatilizing the foreign ingredients,and working the metal to size.

17. The process of producing tungsten metal which comprises mixingtungstic acid with about three percent by weight of normal potassiumtungstate, dehydrating the mixture, subsequently drated mixture oftungstic acid and an alkali tungstate in hydrogen, to form a metallicpowder, compacting said powder to an ingot, baking the ingot inhydrogen, subsequently heating the resultant tungsten and alkalinecompound until the alkali metal oxide compound is completelyvolatilized, and mechanically working the resultant metal to the formdesired.

19. The process of preparing tungsten metal which comprises mixingtogether tungstic acid and an alkaline tungstate solution, heating themixture until the same is dehydrated forming tungsten trioxide (W03) andthe alkaline tungstate, reducing the mixed oxide and tungstate to form amixture of tungsten and alkaline hydroxide, forming the mixed oxide andtungstate into an ingot under pressure, baking the slug to harden thesame, substantially completely volatilizing the. alkaline hydroxide inthe slug, and finally working the resultant metal to size.

20. The process of preparing tungsten metal which comprises mixingvtogether a hydrated tungstic acid having the approximate formula H2WO4and potassium tungstate K2WO4, dehydrating said mixture by heat,reducing said dehydrated mixture in hydrogen to tungsten and potassiumhydroxide, substantially completely volatilizing the hydroxide byheating, and working the resultant metal.

21. The process of preparing tungsten metal which comprises reducing amixture of tungsten trioxide and potassium tungstate to obtain tungstenand potassium hydroxide, forming the mixture into ingot form bypressure, heating the ingot to completely volatilize the hydroxide, andworking the metal to the desired form.

22. The process of preparing tungsten metal which comprises reducing atungsten oxide associated with an alkaline tungstate to a productcontaining tungsten metal and an alkaline hydroxide, forming an ingot ofthe resultant product, substantially completely volatilizing thehydroxide within the slug, and working the ingot to the desired form.

23. A pure tungsten metal consisting of reduction products of tungsticoxide and an alkali metal tungstate and formed of tungsten particles ofconsiderably diiferent sizes welded by chemically deposited tungsten,said tungsten being deposited from a solution in an alkali metal oxidewhich has been completely vaporized at a temperature up to 2000 C., saidpure tungsten in filamentary form being non-offsetting and nonsagging.

24. A pure tungsten metal consisting of reduction products of tungsticoxide and an alkali metal tungstate and formed of particles of tungstenof considerably different sizes bonded by chemically deposited tungsten,said tungsten besagging.

25. A process of preparing tungsten metal, which comprises providing acompacted mass of finely divided tungsten, the particles of whichtungsten are coated with a volatile alkaline metal Y compound, and thenheating the compacted mass in a reducing environmentto volatilize thealkaline compound at a temperature up to above about 2000 C. and belowthe melting point of tungsten,

26. A process of preparing metal tungsten, which comprises mixing atungsten oxide with an alkaline metal compound of a tungsten oxide,reducing the mixture to metallic tungsten and an alkaline metal oxide,and then substantially completely volatilizing oil? the alkaline metaloxide up to a relatively hightemperature above 2000 C.

and below the melting point of tungsten.

, 27. A process of preparing tungsten, which comprises adding about 1000parts of tungstic acid to a solution of about 60 parts of an alkalimetal tungstate in water, dehydrating the mixture and then grinding themixture to about 200 mesh, reducing the mixture in' a hydrogenatmosphere to tungsten and'the alkali metal,

oxide, pressing the reduced mixture to ingot form, baking theingot inhydrogen to about 800 C. and thensubstantially completely volatilizingaway the alkali metal hydroxide up to a temperature above about 2000C.and belowthe melting point of tungsten.

28. A process of preparing metallic tungsten, molybdenum, titanium,tantalum, zirconium and chromium, which comprises mixing an oxide of oneof said metals with an alkali metal salt of 40 said oxide in thepresence of water, removing the 45 in hydrogen at about 800 water andgrinding the dehydrated mass, reducingthe dehydrated mass to the metaland an alkali metal oxygen compound, pressing the reduced mixture .toingot form, baking the ingot 0., and then substantially completelyvolatilizing away the alkali metal oxygen compound in a hydrogenatmosphere up to above about 2000 (Land below the melting .point oftungsten.

selected from the group consisting of tungsten, molybdenum, titanium,tantalum, zirconium and chromium, which comprises mixing an oxide of themetal with an alkaline metal compound containing the refractory metal,reducing the compound to obtain the metal and an alkali metal oxidecompound, compacting the reduced mixture to form an ingot, and finallyheating the metal,

and oxide compoundingot at a temperature in excess of the volatilizationpoint of the oxide compound. j

30. r A process of producing a tungsten filament for electric lamps withnon-sagging characteristics which comprises providing a compactedmixture of metallic tungsten and an alkali metal oxide compound whichhas been produced by the hydrogen reduction of tungsten oxide and analkali metal tungstate, and completely vaporizing ed the alkali metaloxide compound up to a temperature above 2000 and below the meltingpoint of tungsten and in a reducing atmosphere.

31. A pure molybdenum metal consisting of molybdenum particles ofconsiderably difierent sizes, and the particles of said molybdenum beingscoured by complete vaporization of alkali metal oxides in combinationtherewith up to an elevated temperature above 2000 C. and below thefusion point of molybdenum, said molybdenum in filamentary form havingnon-ofisetting and non-sagging characteristics, said molybdenumconsisting of the hydrogen-reduction products of molybdenum oxide and analkali metal molybdate.

32. A process of producing a molybdenum filament for-electric lamps withnon-sagging char- 29. The process of treatingrefractory metal,-

acte'ristics which comprises providing a com- C ESTER H. BRASELTONi

